Apoptosis of vascular smooth muscle cells in neointimal lesions is a newly recognized feature of both atherosclerotic and restenotic lesions. The cause of apoptosis and the role that it plays in lesion development is unclear. Ligand-induced activation of members of the tumor necrosis factor (TNF) receptor family, including TNFR-1, FAS and the p75 neurotrophin receptor (p75NTR) have been implicated in the apoptosis of epithelial cells, lymphocytes and neuronal cells. Several studies have demonstrated the expression TNF, FAS and FAS ligand in atherosclerotic lesions. Studies from our own laboratory have demonstrated the expression of the p75NTR and their ligands, the neurotrophins in vascular lesions. The overall aim of this study is to examine the role of the TNF receptor family in smooth muscle lesions. The overall aim of this study is to examine the role of the TNF receptor family in smooth muscle cell apoptosis, both in vitro and in vivo, and to define the signaling pathways which mediate this response. Experiments in Specific Aim 1 will examine the kinetics of smooth muscle cell death in response to TNFR1, FAS and p75NTR activation and define this death as apoptosis. In Specific Aim II, we will examine the potential signaling pathways which mediate smooth muscle cell apoptosis. The signaling pathways to be examined include activation of the sphingomyelinase/ceramide pathway, the stress activated protein kinases and NFkB. The involvement of the so called death domain adapter proteins, TRADD and FADD will also be examined. Deletion mutants of the cytoplasmic domain of the p75NTR will be examined for their ability to induce specific signaling pathways and mediate apoptosis in response to the neurotrophins. In Specific Aim III, the influence of trk receptors both full length and truncated isoforms, on p75NTR signaling pathways and induction of apoptosis will be assessed. Finally, in Specific Aim IV, the influence of p75NTR, TNFR1 and FAS expression on the lesions which develop following vascular injury in p75NTR null mutant (-/-), TNR1 null mutant (-/-) mice, Ipr (FAS -/-) mice and their normal (+/+) littermates will be determined. The results of these studies will define potential mediators of apoptosis in vascular lesions and the signaling pathways which mediate this response. This may aid in the development of drugs which can inhibit apoptosis, which would then allow studies to assess how apoptosis affects overall lesion development following vascular injury.